1. Field of the Invention
The present invention relates to a median filter for eliminating an impulse noise component corrupting a video signal. More specifically, the present invention relates to a median filter for executing a filtering operation while adaptively changing the size of window for filtering of the video signal. Advantageously, the present invention can be used either in a receiver of FM signals associated with satellite broadcasting or in a television receiver susceptible to receiving an electromagnetic wave containing interference.
Korean Patent Application No 92-20268 is incorporated by reference for all purposes.
2. Description of the Prior Art
In general, an impulse noise component is often added to a video signal of television. The impulse noise in the video signal may be produced by the lower S/N ratio associated with broadcasting of FM signal via satellite as well as provided by an electromagnetic wave interference in a receiver side of television signal. The impulse noise in the FM signal is produced by incongruously tracking an original frequency band of the FM signal the user intends to demodulate within the receiver. The impulse noise from electromagnetic wave is produced by an electric motor and the like, and it can take a band form made of one line or a number of lines. Such an impulse noise produces a portion of the demodulated signal which is incongruous with the original signal.
One proposed solution for eliminating the impulse noise is a median filter. FIG. 1 is a block diagram for schematically showing a conventional median filter. Pixel data, e.g., 8 bits of pixel data D.sub.IN, is continuously applied to and stored in a memory 12. Since the pixel data D.sub.IN consists of 8 bits, one pixel has a resolution of "0-255". The memory 12 supplied with pixel data stores picture data of a predetermined region dictated by memory capacity and supplies the pixel data included in a window of predetermined magnitude, i.e., size, to a sorter 14. The sorter 14 sorts the pixel data supplied from memory 12 according to a magnitude of data, and outputs a median value X.sub.med obtained by sorting. The median value X.sub.med output from the sorter 14 can be expressed as the following expression (1). EQU Xmed=MEDIAN{X.sub.j }.sup..omega..sub.j=1 ( 1)
where .omega. is the number of pixels included in the window.
However, since this conventional median filter includes a fixed window magnitude, which is a unit of data processing, for calculating a median value, it cannot adaptively cope with a distribution change of pixel values. More particularly, where a positive impulse noise and a negative impulse noise are mixed in a video signal subjected to median filtering, the impulse noise eliminating capacity becomes worse. Moreover, when there is no impulse noise in the window data, the edge of the video signal is changed or shifted.